One of my main building goals is to have at least one sizable creation from each of the six Star Wars movies (sizable = bigger then my cat). With the Winter '06/'07 competition at FBTB.net, I finally got inspired for a creation from Episode III. It measures 100 studs across and took about a month and a half to build. It contains roughly 2200 pieces.
The big, round engines were the first thing I made. I wasn't sure what I would make for the competition, but going through the pieces in my collection I got the inspiration of how to create them. The entire ship was then based around the size of the engines I had made. The front of the engine is 10 studs long, so I based the 100 stud width on a bit of fuzzy math.
I have a few comparison pics of my model with pics of the actual 3D model. You may be able to see that the 'real' ship's wings tilt slightly down. I was able to achieve this by making really heavy guns. :)